Christopher is 5 times as old as Ashley and is also 8 years older than Ashley. How old is Christopher?
Solution: We can use the given information to write down two equations that describe the ages of Christopher and Ashley. Let Christopher's current age be $c$ and Ashley's current age be $a$ $c = 5a$ $c = a + 8$ Now we have two independent equations, and we can solve for our two unknowns. One way to solve for $c$ is to solve the second equation for $a$ and substitute that value into the first equation. Solving our second equation for $a$ , we get: $a = c - 8$ . Substituting this into our first equation, we get the equation: $c = 5$ $(c - 8)$ which combines the information about $c$ from both of our original equations. Simplifying the right side of this equation, we get: $c = 5c - 40$ Solving for $c$ , we get: $4 c = 40$ $c = 10$.